The present invention relates to an ink jet head using a piezoelectric body and a manufacturing method thereof, and in particular to an ink jet head using a driving source having a bimorph structure and a manufacturing method thereof.
An ink jet printer carries out printing on sheets by ejecting ink particles from an ink chamber. An ink jet printer has a simpler constitution than an electro-photographic printer, and hence a low-cost printer can be provided. Moreover, color printing is possible with a low-cost apparatus. Ink jet printers thus constitute the mainstream of the low-cost printer market.
Types of ink jet printer are a piezoelectric type that uses a piezoelectric element, and a thermal type that uses a heat-generating element. The piezoelectric type has advantages not seen with the thermal type, namely the response speed is high and the electrical-mechanical energy conversion efficiency is high. The piezoelectric type is thus suited to high-resolution color printers.
With a high-resolution printer, there are problems if the volume of the ink drops is too large or too small. That is, in the case that the volume of the ink drops is too large, the gradation representation ability is insufficient, and hence the resolution drops. Conversely, if the volume of the ink drops is too small, then the printing speed drops, and also the ink flying direction is disturbed due to the influence of air currents and slight electrical charging, and hence the resolution drops. With most high-resolution printers, the volume of the ink drops is thus a few pico-liters (1 pico-liter=10xe2x88x9212 of a liter=10xe2x88x9215 of a cubic meter).
With a piezoelectric body as the driving source for ejecting the ink drops, the mechanical energy generated (generative force) is sufficiently large, but the displacement amount is low. A displacement magnifying mechanism that increases the displacement of the piezoelectric body is thus used. A bimorph structure is most widely used as a suitable displacement magnifying mechanism in an ink jet head.
FIG. 28(A), FIG. 28(B) and FIG. 28(C) are explanatory drawings of a conventional ink jet head. As shown in FIG. 28(A), the bimorph structure has a constitution in which a plate-shaped non-piezoelectric material (metal, ceramic etc.) 91 is stuck onto a plate-shaped piezoelectric body 90. The piezoelectric body 90 expands in the thickness direction, and at the same time contracts in the planar direction, and hence strain arises between the piezoelectric body 90 and the non-piezoelectric material 91, and to relieve this, warping occurs. The radius of curvature due to the warping is somewhat larger on the non-piezoelectric material 91 side (the outside), and is somewhat smaller on the inside of the piezoelectric body 90, and hence the length differs between the outside and the inside of the piezoelectric body 90. A large deformation thus arises for a very small strain (contraction in the planar direction) in the piezoelectric body 90.
An ink jet head using this bimorph driver is shown in FIG. 28(B) and FIG. 28(C). As shown in FIG. 28(B) and FIG. 28(C), nozzles 92 are provided in ink chambers 95 that store ink. A vibrating plate 91 is provided so as to form a wall for the ink chambers 95. The vibrating plate 91 corresponds to the non-piezoelectric material in FIG. 28(A). Piezoelectric bodies 90 are provided on the vibrating plate 91 in correspondence with each of the ink chambers 95. The ink chambers 95 communicate with an ink supply chamber 94 via an ink supply hole 93.
A voltage source 96 is connected between the vibrating plate 91 and the piezoelectric bodies 90, and by supplying a driving voltage, the piezoelectric plates 90 and the vibrating plate 91 are displaced, and pressure is applied to the ink chambers 95. As a result, ink drops are ejected from the nozzles 92 of the ink chambers 95. By releasing the driving voltage, the piezoelectric bodies 90 return to their original positions, and as a result ink is supplied from the ink supply chamber 94 into the ink chambers 95 via the ink supply hole 93.
The displacement amount depends on the width W of the piezoelectric bodies 90 as shown in FIG. 28(B); the displacement amount is sharply reduced if the width W is narrowed. The width W of the piezoelectric bodies 90 thus cannot be made small. The dot pitch of the multi-nozzle head, in which a plurality of the nozzles are arranged in a line, i.e. the nozzle spacing d of the piezoelectric head, is determined by the width W of the piezoelectric bodies 90. An ink jet head using such a bimorph structure is thus greatly inferior to a thermal type in terms of the nozzle installation density (the dot pitch) and the cost. For example, the installation density may be 120 dpi for the piezoelectric body bimorph type compared with 600 dpi for the thermal type, a difference of 5 times.
In the case of the piezoelectric body bimorph type, it is thus necessary to make the width W of the piezoelectric bodies 90 narrower, and hence increase the installation density. However, with the piezoelectric body bimorph type, the width W of the piezoelectric bodies 90 determines the displacement amount, and hence if the width W of the piezoelectric bodies is made narrow, then the displacement amount drops sharply, and stress increases There has thus been a problem in that it is not possible to realize the displacement required for ejecting fine ink drops having a volume suitable for printing (e.g. 1 pico-liter or more). Moreover, there has been a problem that if the driving voltage is increased to increase the displacement amount, then the stress increases, and the vibrating plate 91 breaks.
Moreover, a cantilever beam structure for increasing the displacement amount of a piezoelectric body is known (for example, Japanese Patent Application Laid-open No. 2-143861). FIG. 29(A) and FIG. 29(B) are drawings of the constitution of a conventional cantilever beam structure ink jet head. As shown in FIG. 29(A), a vibrating plate 91, a piezoelectric plate 90 and an individual electrode 98 are provided via an ink chamber 95 on a substrate 97 in which a nozzle 92 is formed. As shown in FIG. 29(B), the piezoelectric body 90 and the vibrating plate 91 have a cantilever beam structure in which only one side is supported. With this cantilever beam structure, the three peripheral edges of the bimorph driver 90 other than the one fixed edge are free edges, and hence there is free entry and exiting of ink to and from the pressure chamber 95. There has thus been a problem that the internal pressure in the pressure chamber does not rise to high, and hence ink drops cannot be accelerated to a sufficient speed.
To increase the pressure in the pressure chamber, one can envisage making the gap around the three edges of the bimorph piezoelectric body 90 narrower. For example, the gap suitable for ink flight is 0.5 microns or less. However, it is virtually impossible to align the various layers with high precision and form such a narrow gap around the three edges of the bimorph piezoelectric body 90. There has thus been a problem that, with an easily realizable gap of about a few microns, ink drops fly at only a very low speed.
It is thus an object of the present invention to provide an ink jet head and manufacturing method thereof for obtaining ink drops of sufficient speed even if the width of the piezoelectric bodies is made narrow.
It is another object of the present invention to provide an ink jet head and manufacturing method thereof for narrowing the width of the piezoelectric bodies, and thus increasing the nozzle installation density of the head.
It is a further object of the present invention to provide an ink jet head and manufacturing method thereof for obtaining sufficient displacement and pressure even if the width of the piezoelectric bodies is made narrow.
Furthermore, it is an object of the present invention to provide an ink jet head and manufacturing method thereof for narrowing the width of the piezoelectric bodies, shortening the time required for ink refilling, and increasing the response frequency.
In one form of the head of the present invention, an ink jet head for ejecting ink drops from a nozzle has a pressure chamber that communicates with the nozzle and stores ink, and a bimorph driver that has a piezoelectric body and a vibrating plate and for applying pressure to the pressure chamber, wherein three peripheral sides of the bimorph driver are fixed and the other one side is not fixed.
With this form, because one side of the piezoelectric body of the bimorph driver is made to be free, pressure leakage can be reduced, and tensile stress can be released. Moreover, because three sides are fixed, pressure leakage can be minimized. The displacement and pressure required for ejecting ink drops can thus be obtained even if the width of the piezoelectric body is narrow. A high-density multi-nozzle head can thus be realized.
In another form of the present invention, the bimorph driver has a slit. with this form, one side of the piezoelectric body of the bimorph driver is made to be free using the slit, and hence the gap at the free edge can be made small, and pressure leakage can be minimized. Moreover, because a slit is used, production is easy.
In another form of the present invention, the slit is provided parallel to the long sides of the bimorph driver. With this form, because the slit is parallel to the long sides of the bimorph driver, deterioration in the ink energy conversion efficiency can be prevented even though the slit is provided.
In another form of the present invention, the slit is provided in the center of the bimorph driver. Because the slit is provided in the center of the bimorph driver, deterioration in the energy conversion efficiency can be prevented even though the slit is provided.
In another form of the present invention, the head further has a filling member for blocking up the slit in the bimorph driver. Because the slit is blocked up with a filling member, ink leakage and pressure leakage can be prevented even though the slit is provided.
In another form of the present invention, the head further has an ink tank that communicates with the pressure chamber via the slit. The slit is used as an ink supply channel, and hence refilling with ink is carried out together with ejection of ink, and thus the response frequency rises, and high-speed printing becomes possible.
A multi-nozzle ink jet head of the present invention has a plurality of pressure chambers that each communicates with a nozzle and stores ink, a plurality of bimorph drivers that each has a piezoelectric body and a vibrating plate and that are for applying pressure to the pressure chambers, and an ink tank that communicates with the plurality of pressure chambers, wherein three peripheral sides of each of the bimorph drivers are fixed and the other one side is not fixed.
With this form, because one side of the piezoelectric body of each bimorph driver is made to be free, pressure leakage can be reduced, and tensile stress can be released. Moreover, because three sides are fixed, pressure leakage can be minimized. The displacement and pressure required for ejecting ink drops can thus be obtained even if the width of the piezoelectric bodies is narrow. A high-density multi-nozzle head can thus be realized.
A method of manufacturing a multi-nozzle head of the present invention has a step of forming in order an electrode layer, a piezoelectric body layer and a vibrating plate layer on one face of a substrate, a step of milling each layer on the substrate to form a plurality of separate bimorph drivers each having a slit, a step of etching the other face of the substrate to form separate pressure chambers, and a step of joining a nozzle plate having a plurality of nozzles onto the substrate.
With this form, because the slits are formed at the same time as forming the individual bimorph drivers through milling, bimorph drivers having one free side can be formed easily and cheaply. Since milling is used, slits of very narrow width can be formed, and hence pressure leakage can be minimized.
In another form of the present invention, the manufacturing method further has a step of filling the slits with a filler after forming the plurality of bimorph drivers. Since the slits are filled with a filler, ink leakage and pressure leakage can be prevented even though the slits are provided.
In another form of the present invention, the manufacturing method further has a step of joining an ink supply member having ink supply chambers to the bimorph drivers after forming the plurality of bimorph drivers. The slits are used as ink supply channels, and hence refilling with ink is carried out together with ejection of ink, and thus the response frequency rises, and high-speed printing becomes possible.